The invention relates to a fixing device of a panel in a receiving groove of a support rail in the form of a U-shaped section extending in the longitudinal direction, said device comprising wedging means collaborating with two adjustment screws to perform vertical securing of the panel in the groove of the support rail, said U-shaped groove being equipped with a rounded bottom and with two divergent ramps arranged at the apex of the opposite two wings of the section,                the wedging means having a cradle straddling the bottom edge of the panel to snugly follow the conjugate shape of the bottom of the groove allowing a rocking movement of small amplitude when angular adjustment is performed.        